Molecularly oriented bottle



2 Sheets-Sheet l Nov. 29, 1966 F. E. WILEY MOLECULARLY ORIENTED BOTTLE Filed July 1, 1965 mer.

A TTORNE V5 Nov. 29, 1966 F. E. WILEY 3,288,317

MOLECULARLY ORIENTED BOTTLE Filed July l, 1965 2 Sheets-Sheet 2 INVENTOR. F.E. WILEY BY f,

A TTORNE V5 United States Patent O 3,288,317 MOLECULARLY ORIENTED BOTTLE Fred E. Wiley, Hazardville, Conn., assigner to Phillips Petroleum Company, a corporation of Delaware Filed July 1, 1965, Ser. No. 472,393 2 Claims. (Cl. 21S-1) This application is a continuation-in-part of my copending application Serial No. 153,355, filed November 20, 1961, and now abandoned.

This invention relates to apparatus for conditioning thermoplastic polymer prior to orientation thereof. In another aspect it relates to a method and apparatus for forming oriented articles of thermoplastic polymer by blow molding. In a further aspect it relates to novel articles formed from oriented thermoplastic polymer. A still further object of this invention is to provide novel articles of oriented polypropylene.

It is well known that many crystallizable thermoplastic polymers such as polyethylene, polypropylene, poly-1- butene, and copolymers of these and higher mono-l-olens can be strengthened by orientation. This molecular orientation can be brought about by stretching the polymeric structure, preferably biaxially at temperatures below the crystalline melting point of the polymer. While these principles can be readily applied to batch operations, the control of continuous processes to produce molecularly oriented structures is more difficult.

I have discovered an apparatus and method for the production of uniquely strengthened hollow articles such as bottles, drums, carboys and the like by blow molding after temperature conditioning the polymer which has been extruded in the form of a tube. According to one aspect of my invention I have provided an apparatus for conditioning an extruded tube of thermoplastic polymer prior to orientation thereof. This apparatus comprises an elongated sizing sleeve which can be fastened to the extrusion die from which the tube issues in combination with means for evacuating the space between the extruded tube and the sleeve wall, means for cooling the extruded tube as soon as it enters the sleeve and means for reheating at least the surface of the tube before it leaves the sleeve. This apparatus can be used to provide a conditioned tube which can be oriented by inflation or drawing over an expander ring. The inflation can be continuous as in the production of lm or it can be carried out intermittently by expanding a parison contained between mold halves to produce hollow articles.

According to another aspect of my invention the above described temperature conditioning sleeve can be used in combination with bottle molding apparatus. This apparatus combination comprises means for extruding a parison, means for cooling the parison, means for reheating the parison, means for pulling the parison from the reheating means, a plurality of bottle molds positioned to close about successive portions of the heated parison, and means for inating each parison portion within a mold by internal uid pressure. According to my 3,288,317 Patented Nov. 29, 1966 ICC invention a method is provided for blow molding hollow articles from thermoplastic crystalline polymer which comprises extruding a parison, cooling the parison until the polymer is in uniform crystalline condition, reheating the parison to within a few degrees below the crystalline melting point of the polymer, passing the parison thus reheated into a mold, and expanding the parison against the wall of the mold by internal iluid pressure. y According to a further aspect of my invention I have discovered that hollow articles produced in accordance with the above aspects possess unique and desirable properties when formed from polypropylene.

It is an object of my invention to provide apparatus suitable for conditioning an extruded tube of thermoplastic polymer prior to orientation thereof by stretching. Another object of my invention is to provide apparatus for the continuous production of hollow articles by blow molding successive portions of an extruded parison. Still another object of my invention is to provide an apparatus and method by which an extruded parison can be conditioned so that when the parison is subsequently blow molded to form a hollow article a satisfactory seal is produced between the inner portions of the parison which are pressed together while the walls of the parison are substantially strengthened by molecular orientation. Other objects, advantages and features of my invention will be apparent to those skilled in the art from the following discussion and drawings of which FIGURE l is an elevation drawing in section of the cooling and reheating sleeve of my invention shown in.

combination with an expander ring for the production of oriented lm;

FIGURE 2 is a schematic drawing in elevation of apparatus for temperature conditioning extruded tube and subsequently molding saine in the shape of a bottle; and

FIGURE 3 is an illustration of a modied form of the cooling and reheating sleeve which minimizes sticking of the tube within the sleeve operating in combination with continuous bottle molding apparatus.

The apparatus and method of my invention can be employed in the fabrication of articles from any thermoplastic polymer which is normally extruded, thermoformed or blow molded, but the invention is of particular advantage with those crystallizable polymers which can be oriented on stretching at carefully controlled temperatures, preferably just below the crystalline melting point of the polymer. Polymers such as polystyrene, polyvinylchloride, nylons and various cellulose derivatives can be fabricated with the apparatus of my invention, but I prefer to work with the normally solid polymers of monol-olens containing up to 8 carbon atoms, and particularly those polymers which have relatively high degrees of crystallinity, for example the high density ethylene polymers and isotactic polypropylene, poly-4-methylpentene-1, polybutene and the like.

I prefer to practice the invention with the olefin polymers having a degree of crystallinity of at least and more preferably at least percent at 25 C. Particularly suitable are the homopolymers of ethylene and copolymers of ethylene with higher mono-l-olefins having a density of about 0.940 to 0.990 grams per cubic centimeter at 25 C.

As used herein the term density refers to the weight per unit volume grams/ cubic centimeter) of the polymer at 25 C. The density of polymer should be determined while the sample of the polymer is at thermal and phase equilibrium. In order to insure this equilibrium it is desirable to heat the sample to a temperature 15 to 25 centigrade degrees above its melting point and allow the sample to cool at a rate of about 2 centigrade degrees/minute to the temperature at which the density is to be measured. Any standard method for determining7 the density of a solid can be used. The crystallinity of the olefin polymers can be determined by X-ray defraction or nuclear magnetic resonance.

Prior to the determination of crystallinity it is desirable that the sample of the polymer be treated for thermal equilibration in a manner described in connection with the density determination. The higher crystalline olefin polymers referred to above do not have a single freezing and melting point but instead have a crystalline freezing point at which maximum crystalline formation occurs upon cooling of the molten polymer and a separate crystalline melting point at which evidence of crystallinity disappears upon heating a sample of the polymer from a cooled crystalline condition. Ordinarily the latter temperature is several degrees above the crystalline freezing point. The crystalline freezing point of these polymers can be determined by melting a sample of the polymer, inserting a thermocouple in the molten polymer and -allowing the polymer to cool slowly. The temperature is recorded and plotted on a chart versus time. The crystalline freezing point is the first plateau in the time-versusternperature curve. For polyethylene having a density of about 0.960 the crystalline freezing point is about 252 F. The crystalline melting point of these polymers can be determined by freezing a small piece of plastic (usually film) under crossed polaroids in a microscope equipped with means for heating the polymer. The specimen is heated slowly and the melting point is the temperature at which birefringence disappears. For polyethylene having a density of about 0.960 the crystalline melting point is ordinarily about 272 F.

The temperature yat which these highly crystalline polymers are stretched is very important if maximum orientation and strengthening of the polymer is to result. For example, it is necessary that polymer be in a substantially crystalline condition, but if the temperature of the polymer is too low the stretching tends to be uneven and the thin wall of the the structure which is formed tends to rupture. It is desirable, therefore, that .at least a portion of the polymer wall be temperature conditioned so that it is in a crystalline state very near the melting point of the polymer crystallites. Apparatus which can be used to accomplish this temperature conditioning is shown in FIG- URE 1.

In FIGURE 1 the crosshead die 10 is equipped with a die tip 11 and the temperature conditioning sleeve is mounted on the die tip so that the tube that is extruded passes -immediately into the sleeve. The temperature conditioning sleeve comprises an elongated cylindrical wall section 12 .against which the extruded tube is pressed by internal fiuid pressure. A jacket 13 completely surrounds the cylindrical wall section and defines between the jacket yand the wall section a plurality of annular cavities. One lof these annular cavities 14 is disposed in the upstream half of the cooling sleeve toward the extrusion die and communicates through a conduit 16 to a source of cooling liquid. For the extrusion of l-olefin polymers such as ethylene polymers or polypropylene where extrusion temperatures in the range of about 350 to 400 F. are employed, water at room temperature, e.g., about F., is suitable for this purpose. This cooling water flows through conduit 16, through annular orifice 14 and discharges through conduit 17. This cool water circulating through the upstream end of the cooling sleeve has sufficiently low temperature that at least the surface of the tube as extruded is quenched and the polymer toward the outside of the tube reaches a crystalline state. As the sleeve passes through this quenching section of the sleeve a temperature gradient develops through the thickness of the tube. In order to make the temperature of the tube more uniform the tube is next passed through the downstream end of the conditioning sleeve where the temperature is controlled by `a heating fiuid which is introduced through conduit 18 and circulates through annular orifice 19 discharging through conduit 20. Hot water under pressure or any other heat transfer medium can be employed for this purpose. For example, when conditioning polyethylene having a density of about 0.960 pressurized water at a temperature of about 235 to 240 F. can be used. Annular cavities 21 .and 22 which are provided between the jacket and the inner wall section of the cooling sleeve are connected to means for drawing a vacuum so that the space between the inner wall of the conditioning sleeve and the tube as extruded can be evacuated. As shown in FIGURE 1 the annular cavity 22 communicates to the space between the sleeve and the tube through a plurality of holes 23. These vacuum connections which are located at the upstream end of the conditioning sleeve and at its mid point permit operation of the extrusion and temperature conditioning so that the tube wall is maintained firmly against the inner surface of the conditioning sleeve, thereby improving heat transfer. Other vacuum connections can be provided if desired and one positioned at the extreme downstream end of the conditioning sleeve is very helpful in starting up the operation.

The temperature conditioned tube emerges from the inner wall 12 of the conditioning sleeve and passes between guide rolls 24. The tube can then be stretched outwardly over expander ring 26 which is supported from the crosshead die by shaft 27. The oriented film 28 can then be pulled to suitable takeup means not shown. This type of operation can be employed to produce clear, tough polyethylene films at draw down ratios of 10:1 or less. Some clarity has been achieved in films as thick as 5 mils. Very high draw down ratios, e.g. as high as :1, can be attained by this method. When operating as shown in `FIGURE 1 it is ordinarily desirable to operate at a relatively high temperature but below the sticking point of the polymer. This is particularly true on start-up in order to facilitate stretching the tube over the expander ring. In many instances, however, the desirable stretching temperature is somewhat above the temperature at which polymer sticking develops. In these cases it is desirable to modify the conditioning sleeve as shown in FIGURE 3 by enlarging the inside diameter of the wall section at the downstream end thereof. Since a vacuum tap is not provided at this point the tube does not come into contact with this portion of the inner 'wall of the conditioning sleeve and the final reheating is carried out by radiation. This section of enlarged diameter is indicated by numeral 29, FIGURE 3. It has also been found that the hot plastic can be passed over a sharp edge, which is prefer- .ably made of an insulating material, without sticking at temperatures where sticking would normally occur in contact with a larger surface. Annular plate 3i! is provided, therefore, at the end of the conditioning sleeve as shown in FIGURE 3. This annular plate serves as a guide for the polymer tube as it issues from the conditioning sleeve. Electrical resistance heaters can be used in place of the hot circulating liquid in the downstream section 29 of the conditioning sleeve.

While the apparatus described above is very useful in the conditi-oning of polymeric tubes which are to be stretched to form oriented lms, the apparatus is also quite useful in conditioning parisons to be used for blow molding. In this application the reheating of the extruded tube can be controlled so that the exterior portion of the tube is ina crystalline condition and is strengthened by orientation while the inside of the tube is maintained relatively tacky and in a scalable condition so that when the molds close about the conditioned tube a `firm seal is developed between the portion of the tube which is pinched shut. Apparatus which can be used in the formation of strengthened containers formed by blow molding is illustrated in FIGURE 2. The thermoplastic polymer is extruded from -crosshead die 31 through die orice 32 into a sizing and cooling sleeve 33. In this arrangement sleeve 33 does not have the reheating function described in connection with the conditioning sleeves of FIGURES 1 `and 3 but instead serves only to quench the extruded tube, or at least the exterior thereof, so that the tube can be passed into water jacket 34 where all the lpolymer in the tube is brought to a uniform crystalline condition. The tube is then pulled from the water jacket by the continuous belts 36 and 37 and pushed into the heating jacket 3S. This heating jacket can comprise `a porous bronze sleeve through which high pressure steam is .blown or through which a hot heat transfer medium is pumped or it can comprise a bath of heating liquid, for example, ethylene glycol. If a bath of this type is used, pressure is maintained on the ethylene `glycol in order to counter balance any internal pressure held within the tube for blowing the tube downstream of the heating bath. In the heating bath the tube is brought to a temperature within a few degrees, for example, within about 15 F. below the crystalline melting point of the polymer. This is the preferred temperature for orientation in order to achieve maximum strengthening effect.

The heated tube can be further conditioned ina porous sleeve 39 which supports the tube as it passes to bottle mold 40. Bottle mold 4@ comprises ltwo mold halves which can be brought together about the heated tube as it passes from the porous sleeve. One end of the tube is pinched shut by the bottom portion 41 of the mold forming the bottom of the bottle. Heating elements 42 can be positioned in this portion of the mold in order to heat the portion of the tube which has been pinched, shut, thereby forming an effective seal. The remainder of the mold is cooled by circulating `a cool iluid through coils 43. After the mold is closed about the extruded tube, internal gas pressure injected at crosshead die 3l forces the tube out against the walls of the mold forming the bottle. Air ring 44 can be provided surrounding the porous sleeve 49 to aid in further temperature conditioning the tube prior to molding. As an yalternative to using pressurized air within the tube, means can be provided within the bottle mold for evacuating the space between 4the tube and the mold walls, thereby vacuum-forming the conditioned tube within the mold.

FIGURE 3 shows still another embodiment which is preferred for the continuous production of relatively small containers. The extruded tube, properly conditioned within the sleeve as previously described, passes directly to molding apparatus 46 which comprises a plurality of mold halves 47 mounted on continuous belts 48 and 49. Belt 48 is mounted on wheels 5i) and 51 while belt 49 is mounted on wheels 52 and 53. As these wheels are rotated the belts move the mold halves 47 into position as shown by mold halves 47a. As these mold halves are brought together they pinch shut a portion of the extruded tube as shown between mold halves 47b. As the closed molds move forward the tube is punctured by needle S4 through which air is injected into the trapped section of the parison as shown between mold halves 47C. The tube is thus forced into conformity with the shape of the mold as shown between mold halves 47d and as the molds move forward the portion of the tube between the molds is severed by knife 56. The mold halves are opened as belts 4i) and 49 pass over wheels 51 and 53 respectively, and the molded bottles are ejected from the mold and fall into a receptacle. In the operation of this apparatus it is desirable to move belts 48 and 49 so that when the mold halves come together a pull is exerted on the parison, moving it forward at a rate which is slightly faster than its rate of extrusion. This subjects the conditioned parison to longitudinal tension and develops a longitudinal molecular orientation within the parison prior to molding. This initial longitudinal stretching strengthens the tube so that it is less likely to rupture or form thin spots on blowing. As discussed in connection with FIGURE 2, lmeans can be provided to draw a vacuum between the entrapped parison sections and the walls of the mold halves. The gas pressure present within the tube at the time the molds closed is trapped within the portion of the tube surrounded by the mold so that evacuating the space between the mold and the parison results in that portion of the parison being forced into conformity with the walls of the mold. By a proper combination of these features, suflicient pressure can be maintained continuously within the extruded parison so that only a slight reduction in the pressure Within the mold is necessary in order to effect the desired inflation of the parison.

Articles such as bottles formed in accordance with the present invention of oriented polymers of l-olens, particularly polypropylene, possess unique properties which in turn enables the articles to be used for many purposes in the art. Such properties include among others orientation release stress, tensile impact strength, and modulus of elasticity in exure.

The following examples are presented in order to illustrate further the method of my invention:

Example I Polyethylene having a density of 0.960 gram per cubic centimeter at 25 C. is extruded continuously in the form of a parison 2 inches in diameter and 47 mils thick. This tube is passed immediately into a conditioning sleeve as shown in FIGURE 3 where it is immediately quenched by water which is circulating through the jacket of the sleeve at 70 F. The surface of the tube is brought quickly |below the sticking temperature and the tube is then reheated to 250 F. in the heating section of the conditioning sleeve. As the tube issues from the sleeve it is stretched longitudinally and then trapped between mold halves which close about the tube completely sealing both ends of the tube which are in the mold. The bottle is then formed by evacuating the space between the mold and the parison causing the parison to be forced into conformity with the mold surfaces. The bottle thus formed possesses molecular orientation within its walls and it is substantially stronger than a bottle formed directly from the hot extruded parison without the temperature conditioning described.

Example Il Blow-molded 10-ounce bottles were made from homopolymer polypropylene and from hornopolymer linear polyethylene. Extruded parisons from each of the two plastic materials were blow-molded to produce both hotblown-blow molded from the parison which was in the d hot-melt state directly after it carne from the extruderand, oriented-blow molded from parisons that had initially cooled to ambient conditions and were reheated to a temperature slightly below the melting point and then blow molded into bottles.

The following table sets forth the basic extrusion conditions and equipment used:

TABLE I.-PARISON EXTRUSION CONDITIONS The basic extrusion conditions and equipment used are listed below:

Polypropylene Polyethylene Barrel temperature, front 430 F Barrel temperature, rear 400 F Die temperature 390 F Takeoil speed. 19 in./min. IIend pressure 2,000 p.s.i. lnternal pressure in pnrison 1 ps1 G p.s.i. Resultant average pnrison wall 0.124 in thickness.

Screw speed 44 r.p.m 44 rpm. P arison cooling Water enscade Water cascade. Sizing method Internal press Internal press.

(C) Parisons for Hot-Blown Bottles:

The following ta'ble sets forth the basic conditions for blow-molding bottles:

TABLE IL BOTTLE BLOW-MOLDING CONDITIONS AND PROCEDURES The basic conditions for lblow-molding bottles are `as follows:

(A) Hot-Blown Bottles:

Parison condition-as extruded Mold assembly-Standard Phillips Petroleum Company lO-ounce bottle mold utilizing 6-inch cylinders for closing pressure.

(l) Polypropylene bottles:

(a) Parison extruded into mold posi-tion and stopped.

(b) Air ilow of 3 c.f.h. applied and closed mold.

(c) Paused 4 seconds and applied 30 p.s.i.g. for

additional 4 seconds.

(d) Removed bottle and repeated procedure.

Note: Mold maintained at room temperature by water cooling.

Polyethylene bottles (a) Parison extruded into mold position and stopped.

(b) Air ow of c.f.h. applied and mold closed.

(c) Paused 1 second andapplied 200 p.s.i.g. for

additional 4 seconds.

(d) Removed bottle and repeated procedure.

Note: Mold maintained at 55 F. by tap Water cooling.

8 (B) Oriented Bottles:

(1) Parison temperature conditioning block.

Material-aluminum Heating methodsteam through cored block ID block-0.865" Interior coating-Teflon Conditions for preheating and blow-molding. Parison length-3 inches Mo1d-standard l0-ounce Phillips Petroleum Company Mold Parison draw-150% Polypropylene Polyethylene Steam pressure on block p.s.i.g 30 p.S.i.g. Parison conditioning time 6 minutes 7 minutes.

Bottles formed under the above conditions were subjected to the following `tests for comparative test evaluation:

TESTS PERFORMED The tests performed for this comparative test evaluation were as follows:

(A) Molding Compound- Pellets as received:

(l) Flow Rate-ASTM Dl238-62T, 230 C.

(a) 2l60-grarn load (b) 21,600-gram load (B) BottlesTeSt specimens `from sidewall:

(l) Density-ASTM D792-60T, Method A, water immersion.

(2) Thickness of sidewalls of bottles used for testing.

(3) Shrinkback-Maximum in both principal directions.

(4) Orientation Release Stress-Maximum in both principal directions; ASTM Dl504-6l.

(5) Orientation Release Temperature at maximum stress in both principal directions; ASTM Dl504- 61.

(6) Tensile Impact Strength in both principal directions at 73 F., 40 F., and 0 F.; DeBell & Richardson, Inc., parallel-strip film-impact test, short specimen.

(7) Flexural Modulus of Elasticity in both principal directions; ASTM D790-63.

(8) Light Transmission-ASTM Dl003-6l, Procedure B (recording spectrophotometer using visual wavelength range of 400-700 millimicrons).

(C) Bottles-As molded:

(l) Drop-Impact Resistance at 73 F. on all bottle types except oriented polyethylene using a bottom drop, a side drop, and a 45degree bottom drop. Also, a bottom drop test was performed at 40 F. on `all bottle types; ASTM D-20 Committee, Proposed Tentative Method of Test for Measuring the Drop Impact Resistance of lBlow-Molded Containers.

(2) Water Vapor Transmission-100 F., 90% relative humidity, with desiccant inside bottle.

TABLE IIL-SUMMARY OF FLOW RATE TESTS [ASTM D 1238, 230 C., 4gram charge] BOTTLES Hot Blown Poly- Oriented Polypropyl- Hot Blown Poly- Oriented Polyethylpropylene ene ethylene ene Property Measured Avg Range Avg. Range Avg. Range Avg. Range Density, 73 F. (g./ec.) 0.903 0. 092-0. 905 0.908 0906-0908 0.946 0. 946-0947 0.956 0954-0957 Wall thickness f bottles used (in.) 0. 014 0. 011-0. 019 0.011 0. 007-0. 018 0.010 0. 008-0. 013 0.007 0. 006-0. 008 Shrinkbaek, maximum (percent):

Circumferential 0. 0 1-15 37 27-45 38 34-42 50 44-53 Axial 4. 0 1-10 37 26-47 14 10-18 54 41-63 Orientation release stress, maximum (p.s.i.)'.

Cireumferential 7. 8 7. 5-8. 0 160 2135-180 1.8 1. 0-2. 6 65 64-65 xial 2. 1. 4-3. 5 155 150-160 No load 52 48 -65 Or(ientation release temp. at maximum stress Cireumierential 325 324-326 322 311-333 286 284-288 277 270-284 Axial 344 343-345 328 313-343 No test 282 278-284 Tensloeimpact strength (it.-lb./in.3):

Cireumferential 160 130-220 780 610-870 270 130-410 530 250-650 0o F Xial 140 110-170 960 770-1, 140 260 160-360 450 420-580 Cireurni'erential 150 180-190 890 570-1, 110 230 150-300 400 220-570 Axial 110 60-140 1, 000 700-1, 200 200 1GO-280 330 170-490 (0,0101l avg. thick.) (0.0095 avg. thick.) (0.0092I avg. thick.) (0.0091l avg. thick.) Light transmission, visible range 1 (percent):

Violet, 400 millimicrons 57. 3 5G. 3-58. 3 82.3 82. 0-82. 6 20. 4 19. 1-21. 7 39.1 38. 5-39. 7 Green, 550 millimierons 65. 1 64. 2-66. 0 86. 6 86. 2-87. 0 26. 8 25. 2-28. 4 63. 8 52. 9-54. 7 Red, 700 millimlerons 68. 66. 9-69. l 87. 5 86. 9-88. l 27. 1 25. 1-29. 1 60. 2 59. 2-61. 2

1 Comparatively, microscope cover glass 0.0085 microns, 91.6%.

TABLE V.-SUMMARY OF TEST RESULTS ON BOTTLES Test Performed Hot Blown Polypropylene Oriented Polypropylene Hot Blown Polyethylene Oriented Polyethylene Drop-impact resistance, water illed (it):

73 F., bottom drop (l0 bottles tested):

Maximum height for Uno failure Minimum height for failure Type of failure 73 F., side drop (10 bottles tested):

Maximum height for "no failure" Minimum height for Iailure Type of failure 73 F., 45 bottom drop (10 bottles tested):

Maximum height for no failure" Minimum height for fai1ure Type of failure F., bottom drop (10 bottles tested) Maximum height for no failure" Minimum height for failure Type of failure Water vapor transmission, g-mil/24 h, 100 F.

90% RH, desiccant inside bottle:

Average Individual values No bottles tested at 73 F.

e Fractured at nip-od seal on bottom.

b Fraetured eireumferentially around bottom.

c Fraetured longitudinally from bottom up.

Examination of the above data clearly demonstrates that:

(1) The processability of the two compounds used in this evaluation is essentially the same. Shear rate--apparent viscosity plots place the two points for each com- (Melt Index 0.8 g. 10 min.) in Bernhardts Processing pound on the same curve as that given for Hi-Fax 1400 of Thermoplastic Materials. At the higher shear rates of normal processing conditions these compounds should show equivalent processability.

(2) Both material types were Ioriented into bottles at temperatures just below the respective melting points to result in what is considered to be maximum orientation. This orientation was measured by the degree of shrinkback and the orientation release stress to establish the fact that significant orientation has been incorporated into the oriented bottles. The orientation in the hot blown bottles is negligible because no signiiicant release stress was obtained even though a fairly high degress of shrink-back was measured in samples from the hot blown polyethylene bottles. This particular shrink-back reects the normal hot melt memory on recovery characteristics of this linear polyethylene, a phenomenon which is not present in the hot melt of polypropylene. This fact is supported by the extrudate diameters from the flow rate tests, which shows the polyethylene to have a significantly larger diameter (0.130" vs. 0.108 for polypropylene).

(3) The impact absorbing qualities in polypropylene is very positively improved by orientation, evidenced by the tensile impact and the bottle drop tests. There is unexpectedly a greater improvement in this respect in the polypropylene than in the polyethylene.

(4) Orientation in polypropylene also creates a toughness that will permit its use at sub-normal temperatures where ordinary unoriented polypropylene could not be used. Essentially the phenomenon of orientation in polypropylene has resulted in the formation of a plastic material significantly different in certain physical and mechanical properties that will allow many applications now not being associated with normal polypropylene.

The clarity of both materials is improved by orientation but the polypropylene has improved as a result of this orientation to a degree that its light transmission in the visible spectrum is approaching that of glass. It is improbable that linear polyethylene will ever approach this degree of clarity regardless of polymer or processing conditions.

(6) Water vapor transmission resistance of the oriented polypropylene bottles is improved over the hot blown bottle to a degree that is considered significant.

The above data was obtained in accordance with the following test procedures. Where applicable, ASTM test procedures were employed. Otherwise, strictly comparative testing was performed, using procedures that were technically valid, giving results that would permit a comparison between the samples and bottles tested. Unless otherwise specified, all tests were performed in an environment of 73 F. and 50% relative humidity with preconditioning of at least 24 hours in the same environment just prior to testing.

(A) Flow Rate: Procedures of ASTM D1238 were followed using a temperature of 230 C., a 4gram charge, and respective weights of 2160 grams and 21,600 grams for the two tests involved. Duplicate tests were performed in each case. The compounds were tested as received in the pellet form. The standard equipment as described in the above ASTM number was utilized with dead weights to apply the load.

(B) Density: ASTM D792-60T, Method A was used. Distilled water was used as the immersion medium and the test sample consisted of the center main section of a bottle measuring about 2.4 inches in the longitudinal direction, and using the full circumference. A small weight was attached to the test sample to make it sink below the water surface, and a small percentage of wetting agent was added to reduce surface tension. Five determinations were made for each bottle type using tive different bottles in each case.

(C) Thickness: All of the bottlese used for this evaluation were checked for profile thickness at three longitudinal points on the bottles. Five measurements were made at each point in the circumferential direction at the center, 1A inch from the botton and 1A: inch from the top of the sidewall. A standard machinists micrometer was used with a ball attachment impinging on the concave surface.

(D) Shrinkback: All of the bottles used for testing were checked for shrinkback characteristics using individual test specimens cut from each principal direction of the bottle. The DeBell & Richardson, Inc., shrinkback tester was utilized with white mineral oil as the immersion medium. These test samples were exposed for a period of 10 seconds at total immersion at temperatures above the respective melting points. For polyethylene this temperature was 300 F., and for polypropylene it was 340 F.

Temperature tolerance during immersion was i2 F. It was determined by trial and error testing that l0 seconds was an adequate time for maximum shrinkback to occur in each case. The test samples were 1A inch wide by 2 inches long. Shrink-back was expressed as the percentage change in length which occurred during this high-temperature irntmersion. Normally mineral oil attacks polyethylene and polypropylene, but the time element was too short for this attack to be effective and possibly `influence shrinkage characteristics. At least one specimen from each principal direction of each bottle evaluated was tested.

(E) Orientation Release Stress, Maximum: Orientation release stress in a stretched plastic sheet is the internal stress which remains frozen into the structure of the material after the manufacturing process. This property was measured -using the essential procedures of ASTM Dl504- 6l. The Instron tester was utilized by clamping a parallelstrip, 1pinch-wide test sample between tensile jaws, and closing the test specimen assembly with a cylindrical heater which was adjusted to give a heating rate of 10 C. per minute. The load imposed by the test specimen was automatically recorded and the maximum load picked from this curve to calculate the maximum orientation stress. Heating rate was controlled manually by adjusting the power input to the cylindrical heater to follow a standard heating curve, which was superimposed on 4the recording monitor that was activated by a low-inertia thermocouple placed within Ma of an inch of the center of the test specimen, but not contacting it. Two determinations were tmade for each bottle type in each principal direction.

(F) Orientation Release Temperature at Maximum Stress: This property was determined during the above orientation release stress testing. The temperature at maximum stress was determined by picking the temperature off the curve plotted on the temperature recorder at the moment maximum load on the test sample was obtained.

(G) Tensile Impact Strength: This property was measured in both principal directions of all bottle types at temperatures of 73 F., 40 F., and 0 F. The test method employed was `the DeBell & Richardson, Inc., parallelstrip tensile impact test using the short specimen. Ten determinations were made for each bottle type in each principal direction. A Baldwin impact tester was utilized with liquid CO2 injection to obtain subnormal testing temperatures. The test specimen and jig holding it were entirely enclosed in the removable environmental chamber `and both maintained at the test temperature for a period of 3 minutes prior to impacting. Prior to any given test series, the specimen-holding jig was cooled to the approximate temperature of testing.

Temperature control was maintained by manual means, adjusting the input of CO2 coolant `to maintain the temperature within i2 of that desired. 'Sample size was 2 inches long by 1A inch wide. Test specimens were carefully prepared by cutting with a new, sharp razor blade and subsequent examination was made of the cut edges under magnification to insure that no edge imperfections were present. All tests used the 4 ft. lb capacity impact hammer.

(H) Flexural Modulus of Elasticity: The procedures of ASTM D790-63 were followed. Test samples were M1 inch wide by 1 inch long cut with a razor blade in both principal directions of the bottle. The span was 0.5 inch using a one-point loading and a radius of nose and supports of 1/16 inch. The Instron tester was utilized for this work, using a load range of 0 to 0.2 pound. A rate of crosshead motion of 0.02 inch per minute was used, and deection of the test specimen was assumed to be essentially identical to crosshead movement, which was used for calculations. Five determinations were made in each principal direction for each bottle type.

(I) Light Transmission: Light transmission was determined on each bottle type 4by using test specimens of approximately the same thickness cut directly from the bottle walls. The test apparatus utilized was a Bausch & Lomb recording spectrophotometer (Spectronic 505), using the visible light range from 400-700 millimicrons. Light transmission was expressed as the percentage of light transmitted through the test sample using a reference beam which represented percent transmission. To aid in comparatively judging the test samples, a comparator of microscope cover glass having an approximating thickness relative to the test samples (0.0085 inch) was used. This testing was performed at ambient room conditions with duplicate determinations being made on separate test specimens. The test samples were tested as cut from the bottle with no effort to Hatten the samples. Thus the natural curvature of the bottle wall was present during these light transmission tests. The values picked for cornparision were those obtained at wavelengths of 400, 550,

13 and 700 millimicrons, respectively representing violet, green, and red.

(I) Bottle-Drop Testing: Bottle-drop impact resistance was determined following the essential procedures of an ASTM D20 Committee Proposed Tentative entitled, Method of Test for Measuring the Drop Impact Resistance of Blow-Molded Containers. This method recommended three types of drops, one on the bot-tom, one on the side, and a LS-degree langle bottom drop. Ten bottles of each type except the oriented polyethylene were drop-impact tested in each recommended position a-t 73 F., using water at the test temperature inside the bottle. The oriented polyethylene was eliminated from lthis test series because of the limited number of bottles available.

The test apparatus for controlling the angle of drop and height consisted of a horizontal trap door arrangement that could be positioned at any height up t-o 12 feet `with a positioning jig which held the bottle in the precise position of drop and a release mechanism that snapped the trap door down and away from the test bottle in such a manner that it allowed lthe bottle to drop freely without rotation to impact in exactly the same position als that held by the bottle when resting on the horizontal trap door. Similar testing was performed at 40 F. using only the bottom drop position, and testing all bottle types.

In each of these tests, for each bottle type, ten samples were tested to obtain the minim-um breaking height range of each. This failure height range was determined by tinding the maximum height at which no fracture occurred and the minimum height at which fracture did occur. The range expressed by these two values is considered to be essentially the minimum failure height range of the bottles. The type of failure in each case was recorded. Each bottle was tightly sealed by a screw cap after completely filling with tap water .at the test temperature.

(K) Bottle Water Vapor Transmission: Water vapor transmission characteristics were determined by exposing the whole bottle yto an environment of 100 F. and 90 percent relative humidity using 150 grams of desiccant (calcium sulfate) inside the bottle and checking weight pickup versus time. Three bottles of each type were so evaluated, using weighing `techniques as recommended by ASTM E96, with at least three successive daily determinations that resulted in essentially a straight-line plot of moisture pickup versus time. determined after the test by dissection and micrometer measurements, and this thickness was included in the cal- Bottle thicknesses were culation-s for water vapor transmission, which were expressed as gram-mil per 24 hours. This thickness consideration in the calculation allowed a direct comparison numerically between bottle types. Bottles were positively sealed lunder a screw cap using a resilient vrubber gasket.

As will be apparent -to those skilled in the art, various modifications can be made `in my invention without departing from the spirit or the scope thereof.

I claim:

1. A molecularly oriented bottle formed from a crystalline polymer of polyethylene, said bottle having a circumferential orientation release stress in the range of 64 to 65 p.s.i., van axial -orientation release stress in the range of 48 to 65 p.s.i., a circumferential modul-us of elasticity in flexure at 73 F. in the range of 2.46 105 to 2.97 105 p.s.i., an axial modulus of elasticity in flexure in the range of 3.61 t-o 4.47X105 p.s.i., a circumferential tensile impact strength at 73 F. in the range of 250 to 650 ft. lb./in.3 and an axial tensile impact strength at 73 F. in the range of 420 to 580 ft. lb./in.5.

2. A molecularly oriented bottle formed from a crystalline polymer of polypropylene, said bottle having a circumferential orientation release stress in the range of to 180 p.s.i., .an axial orientation release stress in the range of to 160 p.s.i., a circumferential modulus of elasticity in flexure at 73 F. in the range of 3.28)( 105 to 4.21 105 p.s.i., `an axial modulus of elasticity in flexure in the range of 3.54 105 to 4.08 105 p.s.i., a -circumferential tensile impact strength at 73 F. in the range of 610 to 870 ft. lb./in.3 and an axial tensile impact strength at 73 F. in the range of 770-1140 ft. lb./in.3.

References Cited by the Examiner UNITED STATES PATENTS 2,616,127 11/1952 Pfeiffer et al. 18-14 2,792,591 5/1957 Cardot et al. 18-5 2,836,318 5/1958 Pinsky et al. 215-1 2,854,691 10/1958 Strong 18-5 2,963,742 12/1960 Ahlich et al. 1814 3,001,239 9/ 1961 Santellic et al. 264-98 3,008,191 11/1961 Park 264-98 3,152,710 10/1964 Platte 2151 JOSEPH R. LECLAIR, Primary Examiner. D. F. NORTON, Assistant Examiner. 

1. A MOLECULARLY ORIENTED BOTTLE FORMED FROM A CYRSTALLINE POLYMER OF POLYETHYLENE, SAID BOTTLE HAVING A CIRCUMFERENTIAL ORIENTATION RELEASE STRESS IN THE RANGE OF 64 TO 65 P.S.I., AN AXIAL ORIENTATION RELEASE STRESS IN THE RANGE OF 48 TO 65 P.S.I., A CIRCUMFERENTIAL MODULUS OF ELASTICITY IN FLEXURE AT 73* F. IN THE RANGE OF 2.46X10**5 TO 2.97X10**5 P.S.I., AN AXIAL MODULUS OF ELASTICITY IN FLEXURE IN THE RANGE OF 3.61X10**5 TO 4.47X10**5 P.S.I., A CIRCUMFERENTIAL TENSILE IMPACT STRENGTH AT 73* F. IN THE RANGE OF 250 TO 650 FT. LB./IN.3 AND AN AXIAL TENSILE IMPACT STRENGTH AT 73* F. IN THE RANGE OIF 420 TO 580 FT. LB/IN.3. 